An internal combustion engine, in particular a reciprocating-piston internal combustion engine, for example on board a motor vehicle, is operated by means of a mixture preparation, wherein the mixture preparation determines a quantity or mass of fuel which is to be injected into the internal combustion engine on the basis of parameters which influence the operation of the internal combustion engine. In addition, the mixture preparation evaluates the signal from a λ probe which is arranged in the exhaust tract of the internal combustion engine and indicates whether the combustion is proceeding in a stoichiometric manner, that is to say neither with excess fuel nor with excess air.
In order to be able to always adapt the internal combustion engine to an extremely wide variety of operating points in an improved manner, operating parameters can increasingly be changed by means of actuators. For example, control times of an inlet valve or an outlet valve, compression of a piston, a proportion of returned exhaust gas can be varied. In addition, there is a further degree of freedom in the case of a so-called dual injection system comprising a combination of intake manifold and direct injection operation. The mixture preparation takes into account the positions of the actuators when determining the quantity of fuel. Remaining deviations which can be attributed, for example, to imperfections of an actuator are corrected on the basis of the λ value.
The λ probe requires a high operating temperature which is usually not yet reached immediately after the internal combustion engine is started. During this phase, the mixture preparation has to carry out a pilot control operation, that is to say determine the quantity of fuel to be injected on the basis of operating parameters of the internal combustion engine, without receiving feedback about the quality of the combustion.
DE 10 2008 012 607 B4 proposes carrying out the pilot control of the mixture preparation on the basis of the main parameters rotation speed, load and temperature. Here, a fixed dependence of the quantity of fuel to be injected on the main parameters is assumed.
However, the actuators are subject to inaccuracies which can have a significant influence on the pilot control. For example, the actual position of an actuator may differ from its intended position owing to wear, scatter or temperature influence. In this case, pilot control can be carried out on the basis of main parameters of the internal combustion engine only with difficulty. The combustion result may be of low quality, with the result that the environmental pollution created by the internal combustion engine increases.